Arthur L. Black

Enzymatic microdetermination of glycogen

Abstract A method for the determination of isolated glycogen was developed. Glucose was released from glycogen with an amyloglucosidase from Rhizopus . The released glucose was determined with glucose oxidase and peroxidase utilizing diammonium 2,2′-azino-di-[3-ethyl-benzthiazoline sulfonate (6)] (ABTS) as a chromogenic substrate. The ABTS method was found to be three times as sensitive as the older o -dianisidine method. For rabbit liver glycogen, the results obtained with amyloglucosidase correlated highly with those obtained by acid hydrolysis.

Glucose as a precursor of milk constituents in the intact dairy cow

Abstract 1. 1. Glucose uniformly labeled with 14 C was injected into the jugular veins of two normal lactating dairy cows as single doses of 3 and 6 microcuries per kg body weight respectively. The injected glucose, about 1 gram, amounted to less than 10% of the plasma glucose. 2. 2. Between 30 and 40 minutes after injection the radioactivity of the respiratory CO 2 reached a maximum of 9 microcuries per unit of the relative injected dose (μc injected per kg body weight). 3. 3. During the first 3 hours after injection of uniformly labeled glucose less 14 C appeared in the respiratory CO 2 than was expired during the corresponding period in earlier trials after injection of 14 C labeled acetate, propionate, or butyrate. 4. 4. More than 50% of the 14 C injected as uniformly labeled glucose appeared in the organic constituents of the milk within 10 hours after injection. Over 80% of this 14 C in milk components was found in lactose. 5. 5. In the first milk sample, 3 hours after injection, the specific 14 C activity in the components of the milk decreased in the following order: Lactose → Citrate → Casein → Milk fat. 6. 6. Only about 1% of the carbon transferred from plasma glucose to lactose passed the carbonate pool, 4 to 10% of the carbon transfer to casein followed this path. 7. 7. Three hours after injection the specific 14 C activity in blood glucose had decreased to about 1% of its theoretical level at the time of injection, the latter calculated from injected dose, plasma volume and glucose level in plasma. 8. 8. About 4 5 of the lactose carbon came from carbon in plasma glucose or a pool in rapid exchange with plasma glucose, 1 5 of the carbon in citrate originated from this pool and about 5% of the carbon in casein and milk fat.

Acetate as a precursor of amino acids of casein in the intact dairy cow.

Five lactating dairy cows were injected intravenously with acetate-I-14C or acetate-2-14C. Eight amino acids, recovered from casein collected at 3, 10, 22, and 34 hours after acetate-14C injection, were assayed for carbon-14. Carbon from acetate was transferred most efficiently to glutamic and aspartic acids and in lesser amounts to alanine, serine, glycine, proline, and arginine. Lysine did not contain significant amounts of 14C. The labeling of amino acids from acetate-14C differed markedly from that previously observed for glucose-14C. Carbon from uniformly labeled glucose was transferred most efficiently to alanine and serine and in smaller amounts to glutamic and aspartic acids, glycine, proline, and arginine. The specific activities of alanine, serine, and lactose were quite similar after acetate-14C injection suggesting a close relationship between the precursors of the three carbon amino acids and lactose. The distribution of 14C among the amino acids formed by the intact cow was consistent with results that would be expected if the TCA cycle and the glycolytic pathway were the pathway for transfer of carbon from acetate to amino acids of casein.

Glucose as a precursor of amino acids in the intact dairy cow.

Abstract A lactating dairy cow was injected intravenously with 2.9 millicuries of uniformly 14C-labeled glucose. The specific activity was determined for plasma glucose and for amino acids of casein during the subsequent 34 hours and these data were used to evaluate glucose as a precursor of amino acids. Glucose carbon was transferred most rapidly and in largest amount to the three carbon amino acids, alanine and serine. Our calculations indicate that 25% of alanine and serine, 10% of aspartic and glutamic acids, and 7% of glycine was derived from plasma glucose. Proposed pathways for the transfer of carbon from glucose to the amino acids are discussed. The amount of glucose carbon transferred to the amino acids via the plasma carbonate pool was evaluated. This indirect pathway, via carbonate, was of minor importance for the non-essential amino acids but was the major pathway for transfer of carbon to the essential amino acids.

WATER TURNOVER IN CATTLE.

The half-life of the body water pool in cattle is unusually short, relative to their body size. The short half-life is not due to milk formation, since the same result is observed in nonlactating cattle as in cattle producing 23 kg (50 lb) of milk per day.

Glucose metabolism in the lactating dairy cow.

Abstract 1. 1. A lactating Jersey dairy cow was injected intravenously with glucose uniformly labeled with 14 C. The rate at which the injected tracer left the blood stream and the amount and speed with which it appeared in the milk and expired air was measured. 2. 2. Our results indicate that in the cow, the metabolic body glucose pool (62 g or less) was about five times as large as the plasma glucose content (12 g). 3. 3. The turnover time for the body glucose pool was less than one hour and the transfer rate of glucose out of this pool greater than 1 g per minute. 4. 4. The lactating cow derived only about 10% of her exhaled CO 2 from pathways involving the oxidation of body glucose to CO 2 . 5. 5. In the energy metabolism of the lactating cow, glucose is relatively less important than it is in the energy metabolism of dogs and rats.

The tricarboxylic acid cycle as a pathway for transfer of carbon from acetate to amino acids in the intact cow.

Abstract Results are presented on the 14 C distribution revealed by the decarboxylation and complete degradation of amino acids recovered from casein after injecting intact cows with acetate-1- 14 C and acetate-2- 14 C. The labeling pattern in the amino acids provides strong evidence for the theory that the Tricarboxylic Acid Cycle is the pathway for transfer of carbon from acetate to amino acids of casein and to lactose. Our studies with acetate- 14 C support the idea that the Tricarboxylic Acid Cycle functions as a pathway of terminal oxidation and also supplies intermediates for the synthesis of milk constituents.

The effect of volatile fatty acids on plasma glucose concentration

Abstract 1. 1. Butyrate causes a marked increase in plasma glucose in lambs and a remission of hypoglycemic convulsions. 2. 2. Propriate causes a similar remission but a considerably smaller plasma glucose increase. 3. 3. Neither of these compounds materially affects plasma glucose levels in other species. 4. 4. Acetate and β-hydroxybutyrate had no effect on plasma glucose concentration in any species. 5. 5. Lamb liver perfusion results were variable as regards a direct action of butyrate on liver glycogen.

The blood precursors of lactose as studied with 14C-labeled metabolites in intact dairy cows★☆

Abstract 1. 1. Lactating dairy cows were injected intravenously with 14 C-labeled carbonate, 1− 14 C acetate, 2- 14 C butyrate, 2- 14 C caproate and U- 14 C glucose. 2. 2. By following the specific activity levels of the plasma glucose and the lactose in the milk over long periods of time, it was possible to calculate that no more than about 85% of the carbon atoms of lactose originated from plasma glucose. 3. 3. Except with acetate as a precursor, lactose synthesis from blood metabolites involved a shorter delay period than any other major milk constituent. 4. 4. The glucose and galactose moieties of lactose were equally labeled, irrespective of time of milk sampling or the 14 C-labeled metabolite injected. 5. 5. It is concluded that besides glucose, other blood metabolites can contribute carbon atoms for lactose synthesis via metabolic pathways which by-pass the plasma glucose pool. However, a single common intermediate for both monosaccharide moieties of lactose appears to exist, presumably within the mammary gland.

Species difference in the glucogenic behavior of butyrate in lactating ruminants

Abstract 1. 1. The hyperglycemia that goats and cows develop in response to intravenous sodium butyrate was investigated during continuous infusion of NaH14CO3 by measuring the transfer quotient to plasma glucose as an index of gluconeogenesis. 2. 2. The results show that a different process occurs in the two species. 3. 3. Goats develop a hyperglycemia as a result of increased glycogenolysis whereas cows respond by increasing gluconeogenesis.